how much are new fan belts plus installation? what about fixing an oil leak?

It depends on whether or not the fan belt is independent of the rest of the belts, or included in an all-in-one (serpentine) belt. If it is independent, it is probably not more than $20 and you can probably replace it yourself quite easily. If it is serpentine then the belt can be $50+, and you will need at least somebody else to help you do it, but if you don't know how to do it, then a mechanic is going to charge you a lot of money for it, you are looking at 2 hours labor easily, if not more.

The oil leak depends on the damage, whether the pan is cracked, a hose is broken, or if it is just a broken seal. Parts are probably not going to be more than $50, the labor is going to be 1-2 hours, depending on how difficult it is to remove the oil pan.

for the fan belt i think the top price is 40 dollars, and for the oil leak it depends of the damage.